Dynamic range explained

Dynamic range (abbreviated DR, DNR,[1] or DYR[2]) is the ratio between the largest and smallest values that a certain quantity can assume. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base-10 (decibel) or base-2 (doublings, bits or stops) logarithmic value of the difference between the smallest and largest signal values.

Electronically reproduced audio and video is often processed to fit the original material with a wide dynamic range into a narrower recorded dynamic range that can more easily be stored and reproduced; this processing is called dynamic range compression.

Human perception

Factor (power)

Decibels

Stops

1

0

0

2

3.01

1

3.16

5

1.66

4

6.02

2

5

6.99

2.32

8

9.03

3

10

10

3.32

16

12.0

4

20

13.0

4.32

31.6

15

4.98

32

15.1

5

50

17.0

5.64

100

20

6.64

1 000

30

9.97

1 024

30.1

10

10 000

40

13.3

100 000

50

16.6

1 000 000

60

19.9

1 048 576

60.2

20

100 000 000

80

26.6

1 073 741 824

90.3

30

10 000 000 000

100

33.2

The human senses of sight and hearing have a relatively high dynamic range. However, a human cannot perform these feats of perception at both extremes of the scale at the same time. The human eye takes time to adjust to different light levels, and its dynamic range in a given scene is actually quite limited due to optical glare. The instantaneous dynamic range of human audio perception is similarly subject to masking so that, for example, a whisper cannot be heard in loud surroundings.

A human can see objects in starlight or in bright sunlight, even though on a moonless night objects receive 1/1,000,000,000 of the illumination they would on a bright sunny day; a dynamic range of 90 dB.

In practice, it is difficult for humans to achieve the full dynamic experience using electronic equipment. For example, a good quality LCD has a dynamic range limited to around 1000:1, and some of the latest CMOS image sensors now have measured dynamic ranges of about 23,000:1.[11] Paper reflectance can produce a dynamic range of about 100:1.[12] A professional video camera such as the Sony Digital Betacam achieves a dynamic range of greater than 90 dB in audio recording.[13]

Audio

Audio engineers use dynamic range to describe the ratio of the amplitude of the loudest possible undistorted signal to the noise floor, say of a microphone or loudspeaker.[14] Dynamic range is therefore the signal-to-noise ratio (SNR) for the case where the signal is the loudest possible for the system. For example, if the ceiling of a device is 5 V (rms) and the noise floor is 10 µV (rms) then the dynamic range is 500000:1, or 114 dB:

20 x log10\left(

\rm5V

10\muV

\right)=20 x log10(500000)=20 x 5.7=114dB

In digital audio theory the dynamic range is limited by quantization error. The maximum achievable dynamic range for a digital audio system with Q-bit uniform quantization is calculated as the ratio of the largest sine-wave rms to rms noise is:

DRADC

=20 x log10\left(

2Q

1

\right)=\left(6.02 ⋅ Q\right)dB

However, the usable dynamic range may be greater, as a properly dithered recording device can record signals well below the noise floor.

Dynamic range in analog audio is the difference between low-level thermal noise in the electronic circuitry and high-level signal saturation resulting in increased distortion and, if pushed higher, clipping.[17] Multiple noise processes determine the noise floor of a system. Noise can be picked up from microphone self-noise, preamp noise, wiring and interconnection noise, media noise, etc.

Early 78 rpm phonograph discs had a dynamic range of up to 40 dB,[18] soon reduced to 30 dB and worse due to wear from repeated play. Vinyl microgroove phonograph records typically yield 55-65 dB, though the first play of the higher-fidelity outer rings can achieve a dynamic range of 70 dB.[19]

German magnetic tape in 1941 was reported to have had a dynamic range of 60 dB, though modern day restoration experts of such tapes note 45-50 dB as the observed dynamic range. Ampex tape recorders in the 1950s achieved 60 dB in practical usage, In the 1960s, improvements in tape formulation processes resulted in 7 dB greater range, and Ray Dolby developed the Dolby A-Type noise reduction system that increased low- and mid-frequency dynamic range on magnetic tape by 10 dB, and high-frequency by 15 dB, using companding (compression and expansion) of four frequency bands. The peak of professional analog magnetic recording tape technology reached 90 dB dynamic range in the midband frequencies at 3% distortion, or about 80 dB in practical broadband applications. The Dolby SR noise reduction system gave a 20 dB further increased range resulting in 110 dB in the midband frequencies at 3% distortion.

Compact Cassette tape performance ranges from 50 to 56 dB depending on tape formulation, with type IV tape tapes giving the greatest dynamic range, and systems such as XDR, dbx and Dolby noise reduction system increasing it further. Specialized bias and record head improvements by Nakamichi and Tandberg combined with Dolby C noise reduction yielded 72 dB dynamic range for the cassette.

A dynamic microphone is able to withstand high sound intensity and can have a dynamic range of up to 140 dB. Condenser microphones are also rugged but their dynamic range may be limited by the overloading of their associated electronic circuitry.[20] Practical considerations of acceptable distortion levels in microphones combined with typical practices in a recording studio result in a useful dynamic range of 125 dB.

In 1981, researchers at Ampex determined that a dynamic range of 118 dB on a dithered digital audio stream was necessary for subjective noise-free playback of music in quiet listening environments.[21]

Since the early 1990s, it has been recommended by several authorities, including the Audio Engineering Society, that measurements of dynamic range be made with an audio signal present, which is then filtered out in the noise floor measurement used in determining dynamic range.[22] This avoids questionable measurements based on the use of blank media, or muting circuits.

Video

When showing a movie or a game, a display is able to show both shadowy nighttime scenes and bright outdoor sunlit scenes, but in fact the level of light coming from the display is much the same for both types of scene (perhaps different by a factor of 10). Knowing that the display does not have a huge dynamic range, the producers do not attempt to make the nighttime scenes accurately dimmer than the daytime scenes, but instead use other cues to suggest night or day. A nighttime scene will usually contain duller colours and will often be lit with blue lighting, which reflects the way that the sensitive rod cells in the human eye sees colours at low light levels.

In digital systems or devices, the ratio of maximum and minimum signal levels required to maintain a specified bit error ratio.

Optimization of bit width of digital data path (according to the dynamic ranges of signal) can reduce the area, cost, and power consumption of digital circuits and systems while improving their performance. Optimal bit width for a digital data path is the smallest bit width that can satisfy the required signal-to-noise ratio and also avoid overflow.[23][24][25][26][27]

In audio and electronics applications, the ratio involved is often large enough that it is converted to a logarithm and specified in decibels.

Metrology

In metrology, such as when performed in support of science, engineering or manufacturing objectives, dynamic range refers to the range of values that can be measured by a sensor or metrology instrument. Often this dynamic range of measurement is limited at one end of the range by saturation of a sensing signal sensor or by physical limits that exist on the motion or other response capability of a mechanical indicator. The other end of the dynamic range of measurement is often limited by one or more sources of random noise or uncertainty in signal levels that may be described as defining the sensitivity of the sensor or metrology device. When digital sensors or sensor signal converters are a component of the sensor or metrology device, the dynamic range of measurement will be also related to the number of binary digits (bits) used in a digital numeric representation in which the measured value is linearly related to the digital number. For example, a 12-bit digital sensor or converter can provide a dynamic range in which the ratio of the maximum measured value to the minimum measured value is up to 212 = 4096.

Metrology systems and devices may use several basic methods to increase their basic dynamic range. These methods include averaging and other forms of filtering, correction of receivers characteristics, repetition of measurements, nonlinear transformations to avoid saturation, etc. In more advance forms of metrology, such as multiwavelength digital holography, interferometry measurements made at different scales (different wavelengths) can be combined to retain the same low-end resolution while extending the upper end of the dynamic range of measurement by orders of magnitude.

Music

In music, dynamic range describes the difference between the quietest and loudest volume of an instrument, part or piece of music.[28] In modern recording, this range is often limited through dynamic range compression, which allows for louder volume, but can make the recording sound less exciting or live.[29]

The term dynamic range may be confusing in music because it has two conflicting definitions, particularly in the understanding of the loudness war phenomenon. Dynamic range may refer to micro-dynamics,[30][31] related to crest factor,[32][33] whereas the European Broadcasting Union, in EBU3342 Loudness Range, defines dynamic range as the difference between the quietest and loudest volume, a matter of macro-dynamics.[34][35][36]

The dynamic range of music as normally perceived in a concert hall does not exceed 80 dB, and human speech is normally perceived over a range of about 40 dB.

Photography

Photographers use "dynamic range" for the luminance range of a scene being photographed, or the limits of luminance range that a given digital camera or film can capture,[37] or the opacity range of developed film images, or the "reflectance range" of images on photographic papers.

Graduated neutral density filters are used to decrease the dynamic range of scene luminance that can be captured on photographic film (or on the image sensor of a digital camera): The filter is positioned in front of the lens at the time the exposure is made; the top half is dark and the bottom half is clear. The dark area is placed over a scene's high-intensity region, such as the sky. The result is more even exposure in the focal plane, with increased detail in the shadows and low-light areas. Though this doesn't increase the fixed dynamic range available at the film or sensor, it stretches usable dynamic range in practice.[40]

Digital imaging algorithms have been developed to map the image differently in shadow and in highlight in order to better distribute the lighting range across the image. These techniques are known as local tone mapping, and usually involves overcoming the limited dynamic range of the sensor by selectively combining multiple exposures of the same scene in order to retain detail in light and dark areas. The same approach has been used in chemical photography to capture an extremely wide dynamic range: A three-layer film with each underlying layer at 1/100 the sensitivity of the next higher one has, for example, been used to record nuclear-weapons tests.[41]

Consumer-grade image file formats sometimes restrict dynamic range.[42] The most severe dynamic-range limitation in photography may not involve encoding, but rather reproduction to, say, a paper print or computer screen. In that case, not only local tone mapping, but also dynamic range adjustment can be effective in revealing detail throughout light and dark areas: The principle is the same as that of dodging and burning (using different lengths of exposures in different areas when making a photographic print) in the chemical darkroom. The principle is also similar to gain riding or automatic level control in audio work, which serves to keep a signal audible in a noisy listening environment and to avoid peak levels which overload the reproducing equipment, or which are unnaturally or uncomfortably loud.

If a camera sensor is incapable of recording the full dynamic range of a scene, high-dynamic-range (HDR) techniques may be used in postprocessing, which generally involve combining multiple exposures using software.

Web site: Sensitivity of Human Ear . The practical dynamic range could be said to be from the threshold of hearing to the threshold of pain [130&nbsp;dB] . 2011-04-21 . live . https://web.archive.org/web/20110604105752/http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earsens.html#c2 . 2011-06-04.

Web site: 24/192 Music Downloads ...and why they make no sense. Montgomery. Christopher. xiph.org. 2016-03-17. The very quietest perceptible sound is about -8dbSPL. live. https://web.archive.org/web/20160314113111/https://xiph.org/~xiphmont/demo/neil-young.html. 2016-03-14.

Web site: What's the quietest sound a human can hear?. Jones. Pete R. November 20, 2014. University College London. 2016-03-16. On the other hand, you can also see in Figure 1 that our hearing is slightly more sensitive to frequencies just above 1 kHz, where thresholds can be as low as −9 dBSPL!. live. https://web.archive.org/web/20160324102019/http://www.ucl.ac.uk/~smgxprj/public/askscience_v1_8.pdf. March 24, 2016.

Web site: Lecture 007 Hearing II. Feilding. Charles. College of Santa Fe Auditory Theory. 2016-03-17. The peak sensitivities shown in this figure are equivalent to a sound pressure amplitude in the sound wave of 10 μPa or: about -6 dB(SPL). Note that this is for monaural listening to a sound presented at the front of the listener. For sounds presented on the listening side of the head there is a rise in peak sensitivity of about 6 dB [−12 dB SPL] due to the increase in pressure caused by reflection from the head.. dead. https://web.archive.org/web/20160507181640/http://www.feilding.net/sfuad/musi3012-01/html/lectures/007_hearing_II.htm. 2016-05-07.

Book: Newman, Edwin B.. American Institute of Physics handbook. 1972-01-01. McGraw-Hill. 978-0070014855. New York. 3–155. English. Speech and Hearing. The upper limit for a tolerable intensity of sound rises substantially with increasing habituation. Moreover, a variety of subjective effects are reported, such as discomfort, tickle, pressure, and pain, each at a slightly different level. As a simple engineering estimate it can be said that naive listeners reach a limit at about 125 dB SPL and experienced listeners at 135 to 140 dB.. 484327.

Web site: 24/192 Music Downloads ...and why they make no sense . Montgomery . Chris . Chris Montgomery . March 25, 2012 . xiph.org . 26 May 2013 . With use of shaped dither, which moves quantization noise energy into frequencies where it's harder to hear, the effective dynamic range of 16 bit audio reaches 120dB in practice, more than fifteen times deeper than the 96dB claim. 120dB is greater than the difference between a mosquito somewhere in the same room and a jackhammer a foot away.... or the difference between a deserted 'soundproof' room and a sound loud enough to cause hearing damage in seconds. 16 bits is enough to store all we can hear, and will be enough forever. . live . https://web.archive.org/web/20130707161555/http://xiph.org/~xiphmont/demo/neil-young.html . 7 July 2013 .

Web site: Coding High Quality Digital Audio . Stuart . J. Robert . 1997 . Meridian Audio Ltd . 2016-02-25 . One of the great discoveries in PCM was that, by adding a small random noise (that we call dither) the truncation effect can disappear. Even more important was the realisation that there is a right sort of random noise to add, and that when the right dither is used, the resolution of the digital system becomes infinite. . dead . https://web.archive.org/web/20160407163817/https://www.meridian-audio.com/meridian-uploads/ara/coding2.pdf . 2016-04-07.